Role of Te/Ti and ∇vtor in ion heat transport of ASDEX Upgrade H-mode plasmas

Experiments in H-mode plasmas have shown that both heat and particle transport are sensitive to the ratio between electron and ion temperature (Te/Ti). While decreasing Te/Ti is beneficial for confinement, an increased electron heating in these so called 'hot ion plasmas' deteriorates the confinement. H-mode plasmas with low Te/Ti are often accompanied by high toroidal rotation velocity (vφ). Its gradient (∇vφ) can destabilize the ion temperature gradient mode (ITG) through its parallel component in the parallel velocity shear, but it has also stabilizing effects since it produces an E x B shearing rate (ωExB). In this paper, the effects of electron heating on the ion heat transport is investigated in H-mode plasmas heated by neutral beam injection (NBI) and electron cyclotron heating (ECH). In particular, the correlation on Te/Ti and ∇vφ is studied and compared with calculations made with GLF23 and GS2. Experimentally it is shown that the normalized gradient length of the ions ( R/LTi) is correlated with both Te/Ti and ∇vφ: peaked ion temperature profiles are only obtained with low Te/Ti and high ∇vφ, and vice-versa. When ECH is added, both ion heat and momentum transport are enhanced, leading to a drop of both the Ti and vφ profiles. The effective growth rate γeff = γ-ωExB is calculated, with the mode growth rate γ determined with GS2 and ωExB with GLF23. The ion transport is enhanced due to the decrease of the ITG R/LTi threshold with increasing Te/Ti. Comparison of the dependence of R/LTi on Te/Ti and ∇vφ between experiments and modelling indicates that the deterioration of confinement cannot be explained by the changes in only Te/Ti or ∇vφ, but by the combined effects of both parameters. The changes in Te/Ti act directly on the ITG threshold, while the ones in ∇vφ modify the ωExB shearing rate leading to changes in the effective threshold